Roll-over suppressing control apparatus for a vehicle

ABSTRACT

The invention provides a roll-over suppressing control apparatus for a vehicle which can suppress roll-over of the vehicle sufficiently also upon steering back turning wherein the turning direction of the vehicle changes over halfway. The roll-over suppressing control apparatus includes a roll-over suppressing control section for controlling, if a roll rate sensor detects that, upon turning of the vehicle, the vehicle is in an excessive rolling state, a braking mechanism so as to apply or increase braking force to a turning outer wheel to perform roll-over suppressing control. If a decision section decides during the roll-over suppressing control that all of the left and right wheels of the vehicle remain in contact with the road, then the roll-over suppressing control section carries out all wheel braking control of controlling the braking mechanism so as to apply the braking force to all of the left and right wheels of the vehicle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a roll-over suppressing control apparatus for a vehicle which causes, when the vehicle is placed into an excessive rolling state upon turning thereof, braking force to be applied to turning outer wheels to carry out roll-over suppressing control.

2. Description of the Related Art

As a technique for controlling the posture of a vehicle upon turning, a technique has been develop wherein a rolling state of the vehicle body is detected and, when the rolling of the vehicle body is excessively great, braking force is applied to particular wheels to suppress rolling of the vehicle thereby to suppress roll-over (turning over on its side) of the vehicle (refer to, for example, Japanese Patent Laid-Open No. Hei 11-11272).

According to the technique, when a roll rate (rolling angular velocity) of the vehicle body is detected and the detected roll rate is equal to or higher than a predetermined value or when a steering angular velocity is arithmetically operated based on a steering angle detected by a steering angle sensor and the value of the arithmetically operated steering angular velocity is equal to or higher than a predetermined value, the brake system of the vehicle is controlled to suppress rolling of the vehicle body.

In order to suppress rolling of a vehicle, it is effective to lower the speed of the vehicle and suppress turning of the vehicle, and it is effective to apply braking force, for example, to front and rear wheels on the turning outer wheel side.

Incidentally, turning which gives rise to roll-over of a vehicle has not only an ordinary type of one-directional turning but also turning wherein the turning direction of a vehicle changes over halfway of turning as a result of a steering back operation of a steering wheel as upon lane change or upon S-shaped curve traveling (the turning is hereinafter referred to as steering back turning). In such steering back turning, a great reactive movement is generated in the rolling direction of the vehicle. In this instance, only if braking force is applied to turning outer wheels of the vehicle described above, there is the possibility that the roll-over may be suppressed sufficiently.

Further, in such steering back turning as described above, since the turning direction changes over halfway, where roll-over suppressing control is being carried out, the turning outer wheels to be controlled change over halfway. However, since response time is required for changeover of braking force, considerable time is required until the braking state to the turning outer wheels to be controlled changes over completely, and consequently, there is the possibility that the roll-over may not be suppressed sufficiently also in this regard.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a roll-over suppressing control apparatus for a vehicle which can suppress roll-over of the vehicle sufficiently also upon steering back turning wherein the turning direction of the vehicle changes over halfway.

In order to attain the object described above, according to the present invention, there is provided a roll-over suppressing control apparatus for a vehicle, comprising a braking mechanism capable of braking left and right wheels of the vehicle separately from each other, rolling state detection means for detecting a rolling state of the vehicle, roll-over suppressing control means for controlling, if it is detected by the rolling state detection means that, upon turning of the vehicle, the vehicle is in an excessive rolling state, the braking mechanism so as to apply or increase braking force to a turning outer wheel to perform roll-over suppressing control, and decision means for deciding whether or not all of the left and right wheels of the vehicle remain in contact with a road during the roll-over suppressing control, the roll-over suppressing control means performing, when it is decided by the decision means that all of the left and right wheels of the vehicle remain in contact with the road, all wheel braking control of controlling the braking mechanism so as to apply the braking force to all of the left and right wheels of the vehicle.

It is to be noted that the state wherein all of the left and right wheels of the vehicle remain in contact with a road signifies a state wherein all of the left and right wheels contact with a sufficient load with the road.

Upon steering back turning wherein the turning direction of a vehicle changes over halfway upon steering back of the steering wheel as in the case of lane change or S-shaped curve traveling, a great reactive movement occurs in the rolling direction of the vehicle, and therefore, only if braking force is applied to turning outer wheels as described above, there is the possibility that roll-over may not be suppressed sufficiently. However, with the roll-over suppressing control apparatus for a vehicle according to the present invention, while the vehicle is in a four-wheel ground contacting state (a state wherein the four wheels contact with a sufficient load with the road) which occurs upon steering back turning, braking force is applied to the four wheels, and consequently, the speed of the vehicle is suppressed, which contributes much to roll-over suppression.

Further, such a four-wheel ground contacting state as described above occurs when the turning outer wheels to which braking force is to be applied change over from one to the other of the left and right wheels halfway during steering back turning, and while the four wheels remain in contact with the road, braking force is applied to all of the four wheels, whereupon a state transition occurs from a state wherein braking force is applied to one of the left and right wheels to another state wherein braking force is applied to the other of the left and right wheels through an intermediate state wherein braking force is applied to all of the four wheels. Consequently, changeover of the braking wheels from one to the other of the left and right wheels can be performed smoothly. Also in this regard, roll-over can be suppressed sufficiently.

Preferably, the decision means decides, where a rolling angle of the vehicle can be estimated to be substantially zero when turning of the vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of the vehicle is changed over halfway, that all of the left and right wheels of the vehicle remain in contact with the road.

Preferably, the decision means estimates that, when turning of the vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of the vehicle is changed over halfway, if the magnitude of a roll rate of the vehicle becomes equal to or higher than a predetermined value set in advance, the rolling angle of the vehicle is approximately zero and decides that all of the left and right wheels of the vehicle remain in contact with the road.

Preferably, the decision means estimates that, when turning of the vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of the vehicle is changed over halfway, if the magnitude of a lateral acceleration of the vehicle becomes lower than a predetermined value around zero set in advance, the rolling angle of the vehicle is approximately zero and decides that all of the left and right wheels of the vehicle remain in contact with the road.

Preferably, the roll-over suppressing control means ends the all wheel braking control after the roll-over suppressing control is carried out for a predetermined period of time set in advance.

The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a control block diagram of a roll-over suppressing control apparatus for a vehicle according to an embodiment of the present invention;

FIG. 2 is a system diagram of the roll-over suppressing control apparatus for a vehicle;

FIGS. 3(a) and 3(b) are schematic views illustrating a relationship between a turning direction of a vehicle which includes the roll-over suppressing control apparatus for a vehicle and braking wheels upon ordinary roll-over suppression control;

FIGS. 4(a), 4(b), 4(c) and 4(d) are diagrammatic views illustrating different control starting conditions by different types of turning by the roll-over suppressing control apparatus for a vehicle; and

FIGS. 5 and 6 are flow charts illustrating roll-over suppressing control by the roll-over suppressing control apparatus for a vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A roll-over suppressing control apparatus for a vehicle according to an embodiment of the present invention is equipped in such a braking system for a vehicle as shown in FIG. 2. Referring to FIG. 2, the braking system for a vehicle includes a brake pedal 1, a master cylinder 2 which operates in an interlocking relationship with an operation of the brake pedal 1, and a hydraulic unit 6 for controlling the brake fluid pressure to be supplied from the master cylinder 2 or a brake fluid reservoir 4 to wheel cylinders of wheel brakes (hereinafter referred to as brakes) 10 for braking wheels (front left and right wheels and rear left and right wheels) 5FL, 5FR, 5RL, 5RR in response to the state of the master cylinder 2 or an instruction from a braking controller (brake ECU) 3. It is to be noted here that a braking mechanism is formed from a liquid pressure adjusting system including the master cylinder 2, hydraulic unit 6 and so forth and the brakes 10 for the braking wheels and so forth.

As seen in FIG. 2 (in FIG. 2, only the left and right wheel brakes for the front wheels are shown), when the vehicle is in a behavior control mode, a differential pressure regulating valve 68 in the hydraulic unit 6 operates so that a predetermined pressure difference may appear between the upstream and the downstream of the differential pressure regulating valve 68.

When the vehicle is in the behavior control mode and the brake pedal 1 is not operated, an in-line intake valve 61 is closed while an out-line intake valve 62 is opened. Consequently, the brake fluid in the brake fluid reservoir 4 is introduced through an out-line 64, the out-line intake valve 62 and a pump 65 and is pressurized by the pump 65, and the pressure of the brake liquid is adjusted by a liquid pressure holding valve 66 and a pressure reducing valve 67 and the brake liquid of the adjusted pressure is supplied to the brakes 10 for the wheels.

When the vehicle is in the behavior control mode and the brake pedal 1 is operated, since the in-line intake valve 61 is opened and the out-line intake valve 62 is closed, the brake fluid in the master cylinder 2 is introduced through an in-line 63, the in-line intake valve 61 and the pump 65 and pressurized by the pump 65. Then, the pressure of the brake fluid is adjusted by the liquid pressure holding valve 66 and the pressure reducing valve 67, and the brake fluid of the adjusted pressure is supplied to the brakes 10 for the wheels.

It is to be noted that the in-line 63 and the out-line 64 join together on the downstream of the in-line intake valve 61 and the out-line intake valve 62, and the pump 65 is disposed on the downstream of the joining location. The liquid pressure holding valve 66 and the pressure reducing valve 67 are provided for each of the braking wheels 5FL, 5FR, 5RL, 5RR on the downstream of the pump 65.

Upon normal braking, the in-line intake valve 61 and the out-line intake valve 62 are closed, and the differential pressure regulating valve 68 and the liquid pressure holding valve 66 are opened while the pressure reducing valve 67 is closed. Consequently, a brake fluid pressure corresponding to the pressure (that is, braking operation force) in the master cylinder 2 is supplied to the brake 10 for each of the wheels through the in-line 63, differential pressure regulating valve 68 and liquid pressure holding valve 66. On the other hand, when an ABS (antilock brake system or antiskid brake system) operates, a brake fluid pressure corresponding to the braking operation force is suitably adjusted through the liquid pressure holding valve 66 and the pressure reducing valve 67 so that each wheel may not be locked.

The in-line intake valve 61, out-line intake valve 62, pump 65, liquid pressure holding valves 66, pressure reducing valves 67 and differential pressure regulating valve 68 of the hydraulic unit 6 having such a configuration as described above are controlled by the brake ECU 3.

Various signals are inputted to the brake ECU 3. In particular, a steering wheel angle signal is inputted from a steering wheel angle sensor 11 provided for a steering wheel, and a yaw rate signal of the vehicle body is inputted from a yaw rate sensor 12 provided on the vehicle body. Further, a roll rate signal of the vehicle body is inputted from a roll rate sensor (rolling state detection means) 13 provided on the vehicle body, and a brake pedal operation signal is inputted from a brake switch 16. Furthermore, a forward-backward acceleration signal and a lateral acceleration signal are inputted from a forward-backward and lateral acceleration sensor 17 provided on the vehicle body, and vehicle speed (wheel speed) signals are inputted from wheel speed sensors 15.

The brake ECU 3 includes such various functional elements as seen in FIG. 1. Referring to FIG. 1, the brake ECU 3 includes a driver operation state inputting section 31 for receiving various information relating to an operation state of the driver as an input thereto, suitably processing the input information and outputting resulting information, a vehicle motion state inputting section 32 for receiving various information relating to a motion state (behavior) of the vehicle, suitably processing the input information and outputting resulting information, and a roll-over suppressing control section 33.

The driver operation state inputting section 31 decides whether or not the brake pedal is operated from a brake pedal operation signal from the brake switch 16 and time differentiates a steering wheel angle based on a steering wheel angle signal from the-steering wheel angle sensor 11 to calculate a steering wheel angular velocity (steering angular velocity).

The vehicle motion state inputting section 32 calculates a vehicle body speed, a roll rate deviation and a lateral acceleration. Although the vehicle body speed is normally calculated based on the wheel speed signals from the wheel speed sensors 15, if a slip occurs with a wheel, then the vehicle motion state arithmetic operation section 32 adds a time integrated value of a forward-backward acceleration obtained from the forward-backward and lateral acceleration sensor 17 to the vehicle body speed obtained till then based on the wheel speed signal to calculate the vehicle body speed (in this instance, the calculated vehicle body speed is an estimated vehicle body speed).

The roll-over suppressing control section 33 includes a turning decision section 34 for deciding a start and an end of turning of the vehicle, a control decision section 35 for deciding a start and an end of roll-over suppressing control, a four-wheel ground contact decision section 36 for deciding whether or not all of the four wheels remain in contact with the ground upon roll-over suppressing control, and a control amount setting section 37 for setting a control amount (roll-over suppressing control braking force) to each braking wheel upon roll-over suppressing control.

The roll-over suppressing control section 33 starts roll-over suppressing control if it is decided by the control decision section 35 that roll-over suppressing control should be started, and ends the roll-over suppressing control if it is decided by the control decision section 35 that the roll-over suppressing control should be ended. Upon such roll-over suppressing control, if all of the four wheels remain in contact with the road, then the roll-over suppressing control section 33 carries out control (all wheel braking control) of applying braking force to all of the four wheels, but if all of the four wheels are not in contact with the road, then the roll-over suppressing control section 33 carries out control of applying braking force to turning outer wheels which remain in contact with the road. The roll-over suppressing control section 33 performs such braking control as just described with a control amount (braking force) set by the control amount setting section 37.

It is to be noted that, in ordinary roll-over suppressing control, braking force is applied to the front and rear wheels which are turning outer wheels as seen in FIG. 3(a) or 3 (b). The magnitude of the braking force applied at this instance is set as a value commensurate with the magnitude of the roll rate R_(r) by the control amount setting section 37. It is to be noted that, while, in order to suppress rolling, it is effective to suppress the yaw rate of the vehicle and suppress the vehicle speed, braking force to the front wheel which is a turning outer wheel contributes much to suppression of the yaw rate of the vehicle while braking force to the rear wheel which is a turning outer wheel contributes much to suppression of the vehicle speed.

The turning decision section 34 decides that turning of the vehicle has been started if both of conditions (i) that the vehicle body speed V_(b) is equal to or higher than a reference value (low speed value set in advance) V₁ and that (ii) the magnitude of the lateral acceleration G_(y) of the vehicle body is equal to or higher than a reference value (fixed value set in advance) G_(y1). Further, if any one of two conditions (iii) that the vehicle body speed V_(b) is lower than a reference value (low speed value determined in advance) V₂ (where V₂<V₁) and (iv) that the magnitude of the lateral acceleration G_(y) of the vehicle body is lower than a reference value (predetermined acceleration set in advance) G_(y2) (where G_(y2)<G_(y1)) is satisfied, then the turning decision section 34 decides that the vehicle has ended the turning.

The control decision section 35 performs roll-over suppressing control in response to the detected roll rate R_(r) when a predetermined control start condition is satisfied. Here, the control start condition resides in satisfaction of a condition that it is decided by the turning decision section 34 that the vehicle is turning and another condition that the magnitude of the roll rate R_(r) which is a value of a parameter corresponding to a rolling state of the vehicle is equal to or higher than a control start threshold value R_(rs)1 set in advance.

Further, the control decision section 35 ends the roll-over suppressing control when a predetermined control end condition is satisfied during the roll-over suppressing control. Here, the control end condition resides in satisfaction of any one of a condition that it is decided by the turning decision section 34 that the vehicle is not turning and another condition that the magnitude of the roll rate R_(r) is lower than a control end threshold value R_(rs) 2 set in advance (R_(rs) 2<R_(rs) 1).

The four-wheel ground contact decision section 36 decides, upon steering back turning (for example, upon lane change or upon S-shaped curve traveling) wherein a steering back operation of the steering wheel is performed during roll-over suppressing control, whether or not all of the four wheels remain in contact with the road under sufficient loads. Here, the four-wheel ground contact decision section 36 makes the decision based on the roll rate. The decision of steering back turning can be made depending upon whether or not the steering wheel angular velocity X has been reversed (the direction has been reversed).

Here, a four-wheel ground contact situation is described.

In particular, if the steering wheel operation and the vehicle speed operation are carried out appropriately, then the magnitude of the roll rate or the magnitude of the roll angle does not become excessive and does not cause turning over of the vehicle on its side as seen, for example, in FIG. 4(c) or 4(d). However, if the steering wheel operation and the vehicle speed operation are not carried out appropriately, then the magnitude of the roll rate or the magnitude of the roll angle becomes excessive and sometimes causes turning over of the vehicle on its side as seen, for example, in FIG. 4(a) or 4(b).

For example, in ordinary turning (one-directional turning) which does not involve a steering back operation of the steering wheel, the steering wheel angle α increases in one direction as indicated by a solid line curve LH1 in FIG. 4(a). At this time, the roll rate R_(r) increases suddenly to the turning outer side as the steering wheel angle a increases (that is, upon turning of the steering wheel) as indicated by another curve LR1. If the magnitude of the roll rate R_(r) exceeds a limit, then the magnitude of the roll angle increases as indicated by a curve LA1 and may cause turning over of the vehicle on its side as indicated by a reference character A [refer to FIGS. 4(a) and 4(b)].

On the other hand, in steering back turning wherein turning back of the steering wheel is performed (for example, upon lane change or upon S-shaped curve traveling), the steering wheel angle a is directed in the reverse direction halfway as indicated by a curve LH2. At this time, the roll rate R_(r) increases suddenly to the outer side of the steering back turning as the steering wheel angle α increases in the reverse direction (that is, upon starting of steering back turning) as indicated by a curve LA2 and sometimes causes turning over of the vehicle on its side as indicated by a reference character B [refer to FIGS. 4(a) and 4(b)].

In such steering back turning as described above, since the turning direction changes halfway, also the turning outer wheels changeover. For example, if steering back of the steering wheel is performed to change the turning direction from left turning to right turning, then upon the left turning in the beginning, the vehicle weight is biased to the right wheels which are turning outer wheels, but when the right turning is performed later as a result of the steering back, the vehicle weight is biased to the left wheels which now are turning outer wheels. When the bias of the vehicle weight changes over from the right wheel side to the left wheel side or reversely from the left wheel side to the right wheel side, naturally a state wherein the four wheels contact with a sufficient load with the road (the state is hereinafter referred to as “four-wheel ground contacting state”) occurs halfway during the changeover.

The four-wheel ground contact decision section 36 decides whether or not the wheel is in such a four-wheel ground contacting state.

The four-wheel ground contacting state wherein the four wheels contact with a sufficient load with the road corresponds to a state wherein the magnitude of the steering wheel angle is small or a state wherein the magnitude of the rolling angle is small, and corresponds, if attention is paid to the roll rate, to a state wherein the magnitude of the roll rate increases to some degree after the steering back of the steering wheel.

Therefore, the four-wheel ground contact decision section 36 determines that “the vehicle is in the four-wheel ground contacting state wherein the four wheels contact with a sufficient load with the road” when the magnitude of the detected roll rate R_(r) is equal to or greater than a four-wheel ground contact decision roll rate threshold value R_(rs) 3 set in advance. It is to be noted that, although the four-wheel ground contact decision roll rate threshold value R_(rs) 3 is generally higher than the control start threshold value R_(rs) 1 (R_(rs) 1<R_(rs) 3), in order to hasten the start of four-wheel ground contact control, the four-wheel ground contact decision roll rate threshold value R_(rs) 3 and the control start threshold value R_(rs) 1 may be set otherwise so as to satisfy R_(rs) 3<R_(rs) 1.

Upon roll-over suppressing control, the control amount setting section 37 normally sets, that is, unless it is decided by the four-wheel ground contact decision section 36 that the vehicle is in a four-wheel ground contacting state, the control amount setting section 37 sets the control amount (roll-over suppressing control braking force) to each of turning outer wheels in response to the roll rate and so forth so that braking force may be applied to the turning outer wheels. On the other hand, if it is decided by the four-wheel ground contact decision section 36 that the vehicle is in the four-wheel ground contacting state, then the control amount setting section 37 sets the control amount (roll-over suppressing control braking force) to each of the four wheels in response to the roll rate and so forth so that braking force may be applied to all of the four wheels. Naturally, the control amount need not necessarily correspond to the roll rate but may be a predetermined value set in advance. Further, the state wherein braking force is applied to all of the four wheels continues only for a predetermined period of time (very short time period) set in advance, and thereafter, until the roll-over suppressing control in the current control cycle comes to an end, the decision of the four-wheel ground contact decision section 36 is not performed and ordinary roll-over suppressing control, that is, control of applying braking force to turning outer wheels, is carried out.

Since the roll-over suppressing control apparatus for a vehicle according to the embodiment of the present invention is configured in such a manner as described above, it carries out its control, for example, in such a manner as illustrated in FIGS. 5 and 6.

Referring first to FIG. 5, a parameter necessary to start or end roll-over suppressing control is inputted at step A5. Then at step A10, it is decided based on a flag F1 whether or not roll-over suppressing control is being carried out. The flag F1 used for the decision is a flag (roll-over suppressing control carrying out flag) indicative of whether or not roll-over suppressing control is being carried out and initially has a value set to zero. Here, if F1=0, then since roll-over suppressing control is not being carried out, the processing advances to step A20, at which a starting condition of roll-over suppressing control is decided. On the other hand, if F1=1, then since roll-over suppressing control has been started already, the processing advances to step A50, at which an ending condition of the roll-over suppressing control is decided.

At step A20, it is decided from the decision condition described above based on the parameter inputted at step A5 whether or not the starting condition of roll-over suppressing control is satisfied. If this condition is satisfied, then the processing advances to A30, at which the flag F1 is set to 1 (on). Then at step A40, roll-over suppressing control is started, and then the flow is ended. However, if the condition is not satisfied, then the flow is ended without changing the flags and the control.

On the other hand, if the decision at step A10 is F1=1, then it is decided at step A50 from the decision condition described above based on the parameter inputted at step A5 whether or not the ending condition of the roll-over suppressing control is satisfied. If this condition is satisfied, then the processing advances to step A60, at which the flag F1 is set to 0. Then at step A70, the roll-over suppressing control is ended, and the flow is ended thereby. However, if the condition described above is not satisfied, then the flow is ended without changing the flags and the control.

The roll-over suppressing control is illustrated in FIG. 6. Referring to FIG. 6, first at step B10, a parameter necessary to decide a start or an end of roll-over suppressing control is inputted. Then at next step B20, it is decided whether or not the roll-over suppressing control carrying out flag F1 is 1. If the flag F1 is 1, then the processing advances to step B30, at which it is decided whether or not another flag F2 is 1.

The flag F2 used for the decision is a flag (four-wheel ground contact control carrying out flag) indicative of whether or not four-wheel ground contacting control, that is, braking force application control to the four wheels for roll-over suppression, is being carried out and whether or not the four-wheel ground contacting control has been carried out already. The flag F2 initially has a value 0 set thereto, but when four-wheel ground contacting control is carried out, the flag F2 is set to a value of 1, and if four-wheel ground contacting control is carried out once and then completed while the roll-over suppressing control is continuing, then the flag F2 is set to another value of 2.

If the flag F2 is not 1 at step B30, then the processing advances to step B40, at which it is decided whether or not the current turning is lane change (steering back turning) depending, for example, upon whether or not the steering wheel angular velocity X has been reversed (whether or not the direction has been reversed).

Here, if the current turning is not lane change (steering back turning), then the processing advances to step B120, at which a control amount (braking force to be applied) for ordinary roll-over suppressing control, that is, for control for applying braking force to turning outer wheels, is set in response to the roll rate, and braking control is carried out based on the control amount (step B130).

If it is decided at step B40 that the current turning is lane change (steering back turning), then the processing advances to step B45, at which it is decided whether or not the flag F2 is 0. If it is decided at step B45 that the flag F2 is not 0, then the processing successively advances to B120 and to step B130 so that ordinary roll-over suppressing control is carried out similarly as described above. If it is decided at step B45 that the flag F2 is 0, then the processing advances to step B50, at which it is decided whether or not the vehicle is in a four-wheel ground contacting state. In this decision, if the roll rate R_(r) detected is equal to or higher than the four-wheel ground contact decision roll rate threshold value R_(rs) 3 set in advance, then it is determined that “the vehicle is in the four-wheel ground contacting state wherein the four wheels contact with a sufficient load with the road”.

If it is decided at step B50 that the vehicle is not in a four-wheel ground contacting state, then the processing successively advances to step B120 and to B130 so that ordinary roll-over suppressing control is carried out similarly as described above.

On the other hand, if it is decided at step B50 that the vehicle is in a four-wheel ground contacting state, then the processing advances to step B60, at which the flag F2 is set to 1, and then to step B70, at which counting of a timer is started. Then at step B80, it is decided whether or not the thus counted timer value is lower than a predetermined value set in advance.

If the timer value is lower than the predetermined value, then the processing advances to step B90, at which a control amount (braking force to be applied) is set in response to the roll rate in order to apply braking force to the four wheels in conformity with the four-wheel ground contacting state and braking control is carried out based on the control amount (step B130).

If the timer value is equal to or higher than the predetermined value, then the processing advances from step B80 to step B100, at which the flag F2 is set to 2, and then to step B110, at which the counting of the timer is stopped and the timer is reset to 0. Then, the processing successively advances to step B120 and to step B130 so that ordinary roll-over suppressing control is carried out similarly as described above.

It is to be noted that, when the roll-over control is ended (when the flag F1 is set to 0), also the flag F2 is reset to 0 (step B140).

In this manner, when lane change (steering back turning) is carried out during roll-over suppressing control or when roll-over suppressing control is carried out as a result of lane change (steering back turning), the four-wheel ground contacting state wherein the four wheels contact with a sufficient load with the road occurs halfway. Thus, this four-wheel ground contacting state is detected, and thereafter, braking force is applied to the four wheels to reduce the vehicle speed to suppress occurrence of rolling for a predetermined period of time. Thereafter, at or around a timing at which the wheels to which the vehicle weight is applied are biased to the turning outer wheel side, if the roll-over suppressing control is required further, then normal control wherein braking force is applied only to the turning outer wheels is restored.

Accordingly, while the road ground contacting load is taken into consideration, roll-over can be suppressed by suppressing the vehicle speed sufficiently through four-wheel braking when the four wheels remain in contact with the road with a sufficient load. However, when only the turning outer wheels contact with a sufficient load with the road, suppression of the yaw moment and suppression of the vehicle speed can be performed efficiently to suppress roll-over by applying braking force only to the turning outer wheels.

Further, since the four-wheel ground contacting state occurs when the turning outer wheels to which braking force is to be applied halfway of steering back turning change over from one to the other of the left and right wheels, by applying braking force to all of the four wheels while the four wheels remain in contact with the road, the state transition occurs from a state wherein braking force is applied to one of the left and right wheels to another state wherein braking force is applied to the other of the left and right wheels through an intermediate state wherein braking force is applied to all of the four wheels. Consequently, changeover of the braking wheels from one to the other of the left and right wheels can be performed smoothly. Also in this regard, roll-over can be suppressed sufficiently.

While a predetermined embodiment of the present invention is described above, the present invention is not limited to the embodiment specifically described above, and variations and modifications can be made without departing from the scope of the present invention.

For example, while, in the embodiment described above, the four-wheel ground contact decision is performed based on the roll rate upon steering back turning, the four-wheel ground contact decision is not limited to this but may be performed based on, for example, the lateral acceleration or the rolling angle of the vehicle. In short, since the four-wheel ground contacting state is established when the lateral acceleration or the rolling angle is small, if the lateral acceleration or the rolling angle is smaller than a threshold value set in advance, then it may be decided that the vehicle is in the four-wheel ground contacting state.

Further, while, in the embodiment described above, four-wheel ground contacting control wherein braking force is applied to all of the four wheels is carried out for a predetermined period of time set in advance after the four-wheel ground contact decision is made, alternatively such logic may be employed that four-wheel ground contacting control wherein braking force is applied to all of the four wheels is started after the four-wheel ground contact decision is made and, when a state wherein the four-wheel ground contacting state is lost, that is, a state wherein the vehicle weight is applied principally to turning outer wheels, is entered thereafter, the four-wheel ground contacting control is ended. In this instance, whether or not the state wherein the vehicle weight is applied principally to turning outer wheels is entered may be decided based on such a parameter as the roll rate, lateral acceleration or rolling angle. 

1. A roll-over suppressing control apparatus for a vehicle, comprising: a braking mechanism capable of braking left and right wheels of said vehicle separately from each other; rolling state detection means for detecting a rolling state of said vehicle; roll-over suppressing control means for controlling, if it is detected by said rolling state detection means that, upon turning of said vehicle, said vehicle is in an excessive rolling state, said braking mechanism so as to apply or increase braking force to a turning outer wheel to perform roll-over suppressing control; and decision means for deciding whether or not all of said left and right wheels of said vehicle remain in contact with a road during the roll-over suppressing control; said roll-over suppressing control means performing, when it is decided by said decision means that all of said left and right wheels of said vehicle remain in contact with the road, all wheel braking control of controlling said braking mechanism so as to apply the braking force to all of said left and right wheels of said vehicle.
 2. The roll-over suppressing control apparatus for a vehicle as claimed in claim 1, wherein said decision means decides, where a rolling angle of said vehicle can be estimated to be substantially zero when turning of said vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of said vehicle is changed over halfway, that all of said left and right wheels of said vehicle remain in contact with the road.
 3. The roll-over suppressing control apparatus for a vehicle as claimed in claim 2, wherein said decision means estimates that, when turning of said vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of said vehicle is changed over halfway, if the magnitude of a roll rate of said vehicle becomes equal to or higher than a predetermined value set in advance, the rolling angle of said vehicle is approximately zero and decides that all of said left and right wheels of said vehicle remain in contact with the road.
 4. The roll-over suppressing control apparatus for a vehicle as claimed in claim 2, wherein said decision means estimates that, when turning of said vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of said vehicle is changed over halfway, if the magnitude of a lateral acceleration of said vehicle becomes lower than a predetermined value around zero set in advance, the rolling angle of said vehicle is approximately zero and decides that all of said left and right wheels of said vehicle remain in contact with the road.
 5. The roll-over suppressing control apparatus for a vehicle as claimed in claim 1, wherein said roll-over suppressing control means ends the all wheel braking control after the roll-over suppressing control is carried out for a predetermined period of time set in advance.
 6. A roll-over suppressing control apparatus for a vehicle, comprising: a braking mechanism capable of braking left and right wheels of said vehicle separately from each other; a rolling state sensor for detecting a rolling state of said vehicle; and a braking controller for controlling, if it is detected by said rolling state sensor that, upon turning of said vehicle, said vehicle is in an excessive rolling state, said braking mechanism so as to apply or increase braking force to a turning outer wheel to perform roll-over suppressing control; said braking controller deciding whether or not all of said left and right wheels of said vehicle remain in contact with a road during the roll-over suppressing control, said braking controller performing, when it is decided that all of said left and right wheels of said vehicle remain in contact with the road during the roll-over suppressing control, all wheel braking control of controlling said braking mechanism so as to apply the braking force to all of said left and right wheels of said vehicle.
 7. The roll-over suppressing control apparatus for a vehicle as claimed in claim 6, wherein said braking controller decides, where a rolling angle of said vehicle can be estimated to be substantially zero when turning of said vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of said vehicle is changed over halfway, that all of said left and right wheels of said vehicle remain in contact with the road.
 8. The roll-over suppressing control apparatus for a vehicle as claimed in claim 7, wherein said braking controller estimates that, when turning of said vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of said vehicle is changed over halfway, if the magnitude of a roll rate of said vehicle becomes equal to or higher than a predetermined value set in advance, the rolling angle of said vehicle is approximately zero and decides that all of said left and right wheels of said vehicle remain in contact with the road.
 9. The roll-over suppressing control apparatus for a vehicle as claimed in claim 7, wherein said braking controller estimates that, when turning of said vehicle during the roll-over suppressing control is steering back turning wherein the direction of the turning of said vehicle is changed over halfway, if the magnitude of a lateral acceleration of said vehicle becomes lower than a predetermined value around zero set in advance, the rolling angle of said vehicle is approximately zero and decides that all of said left and right wheels of said vehicle remain in contact with the road.
 10. The roll-over suppressing control apparatus for a vehicle as claimed in claim 6, wherein said braking controller ends the all wheel braking control after the roll-over suppressing control is carried out for a predetermined period of time set in advance. 